Bag sealing apparatus

ABSTRACT

Bag sealing apparatus comprises a compressed air source which pumps air through a supply pipe towards an opening in a bag. Bag material is advanced by rollers from a roll. The material is in the form of two layers open at one side. The supply pipe extends between the layers through the open side and the open side is sealed by heat sealing by two side members. Each of the rollers defines a circumferential recess and the two recesses together receive the supply pipe. The apparatus further comprises heat sealing elements for sealing the opening in the bag and spring mounted clamp parts for clamping the bag downstream of the sealing elements to reduce fluid back pressure from the downstream bag.

The invention relates to bag sealing apparatus.

It is known to produce air bags, or air pillows, for use in packaginggoods to protect them. Thus, a delicate article might be surrounded withair pillows in a cardboard box to protect it from damage duringtransport. It is known to make such air pillows from heat sealableplastics material and the bags are produced in a strip with each bagbeing heat sealed from the next. The known sealing method is unreliablehowever as the back pressure from air in the bag as it is being sealedtends to unseal the bag.

According to one aspect of the invention there is provided bag sealingapparatus comprising a fluid source to pump fluid towards an opening ina bag, means for sealing the opening in the bag and means for clampingthe bag downstream of the sealing means to reduce fluid back pressure.

In this way, as the bag is clamped downstream of the sealing means, theback pressure does not operate on the seal and a good seal can bereliably ensured. Also the quantity of fluid introduced into the bag canbe closely controlled as fluid cannot escape past the clamping meansduring sealing.

The fluid source may be a source of compressed gas, preferablycompressed air.

The sealing means may seal the bag in any suitable way, such as byadhesive or mechanical means, but preferably the sealing means comprisesheat sealing means.

The clamping means may comprise a resilient member which is urgedagainst the bag. The resiliency aids in providing a fluid tight seal.Preferably, the clamping means comprises two resilient clamping membersarranged on opposite sides to clamp a bag between them.

Preferably, the clamping means is arranged to clamp the bag before thesealing means starts to seal the bag.

The clamping means and sealing means may be mounted separately, but inone embodiment, a clamping member of the clamping means and a sealingmember of the sealing means are mounted together on a mounting member.Preferably, on the mounting member, the clamping member is resilientlymounted ahead of the sealing member so as to engage the bag before thesealing member. This ensures that the bag is clamped before the sealingoperation commences. Preferably, a second mounting member is providedwhich mounts a second clamping member and/or a second sealing member.Conveniently, only one of the first and second mounting members ismovable, but in another embodiment both of the first and second mountingmembers may be movable towards and away from each other. The or eachmounting member is preferably moved pneumatically.

The fluid source may be arranged to pump fluid through a fluid supplypipe.

The apparatus may be arranged to operate in a cycle. The material forthe bag may be provided as a strip which is advanced by advancing meansthrough the apparatus.

The means for advancing the bag material may take any suitable form andpreferably comprises two rollers side by side between which the materialpasses. Preferably, at least one of the rollers includes acircumferential recess and the recess or both recesses together receivethe supply pipe.

The bag material may be in the form of two layers open at one side andthe fluid supply pipe may extend between the layers through the openside. Means is preferably provided for sealing the open side.

According to another aspect of the invention there is provided apparatusfor making a bag comprising means for advancing material for making abag from a store, the material being in the form of two layers open atone side, a supply pipe extending between the layers through the openside and means for sealing the open side.

This arrangement allows the bag to be filled directly and withoutcomplication.

The material may be open at both sides but preferably is open on onlyone side. The open side of the material is preferably sealed upstream ofthe end of the supply pipe. The side sealing means may take any suitableform and may comprise heat sealing means. The side sealing meanspreferably comprises a member which is movable towards and away from theside of the material. The apparatus preferably includes bag sealingmeans for sealing the bag after the bag has been filled from the supplypipe. The bag sealing means preferably lies downstream of the advancingmeans. The bag sealing means preferably includes a member which ismovable towards and away from the material. The bag sealing means andthe side sealing means are preferably rigidly connected and movedtogether. The bag sealing means member and/or the side sealing meansmember may be moved by pneumatic means.

The means for advancing the bag material may take any suitable form andpreferably comprises two rollers side by side between which the materialpasses. Preferably, at least one of the rollers includes acircumferential recess and the recess or both recesses together receivethe supply pipe.

According to a further aspect of the invention there is providedapparatus for making a bag comprising a compressed fluid supply pipe andtwo rollers arranged side by side and between which material for makinga bag passes, one or both of the rollers including a circumferentialrecess and the recess or both recesses together receiving the supplypipe.

In this way the amount of fluid entering the bag can be preciselycontrolled as backflow past the rollers is limited. Preferably thesupply pipe substantially fills the recess or both recesses. The bagmaterial may be provided as a strip. Preferably bag sealing means isprovided immediately past the rollers. Thus, the bag sealing will leaveonly a minimal amount of fluid between the seal and the rollers.Preferably clamping means is provided for clamping a bag downstream ofthe sealing means to reduce fluid back pressure.

Two embodiments of the invention will now be described by way of exampleand with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of the apparatus of the first embodiment;

FIG. 2 is a detail side elevation of the heat sealing part of theapparatus of FIG. 1; and,

FIG. 3 is the view of FIG. 2 of the second embodiment.

FIG. 1 shows the apparatus 10 of the first embodiment. A roll of bagmaterial 12 is stored on a spindle and material 14 from the roll passesover an upper roller 16 and downwardly between two advancing rollers 18which grip the material and are driven by a motor (not shown) to advancethe material in steps. The material is in two layers with a fold on oneside and being open at the other side.

A pneumatic source powers two pistons 20 provided beneath the advancingrollers 18. At the inner end of each piston 20 is connected a bagsealing member 22 parallel to and beneath one of the advancing rollers18. The outer end of each piston 20 is connected to an arm 24 whichextends upwardly past the advancing rollers 18 and inwardly to mount anupright side member 26. One side member 26 includes a heating element 28and the other side member 26 mounts a sprung mounted part 30. Acompressed air supply pipe 32 extends inwardly parallel to the advancingrollers 18 so as to lie between two layers of the material 14 centrallythereof and turns to extend downwardly past the upright members 26 tothe advancing rollers 18. Each advancing roller 18 includes a centralcircumferential recess 34 such that the material and the end of thesupply pipe 32 can be received in the recesses 34. The end of the supplypipe 32 does not extend downwardly past the plane containing the axes ofthe advancing rollers 18.

The bag members 22 are shown in detail in FIG. 2. One of the bag members22 mounts two vertically spaced heating elements 36. The other bagmember 22 carries two spring mounted parts 38 opposite the heatingelements 36. Between the spring mounted parts 38 is provided a serratedblade 40. Below the heating elements 36, the bag member 22 mounts aprojection 42 with a resilient end and a similar projection 42 with aresilient end is spring mounted in an oppositely disposed position onthe other bag member 22. These parts are arranged such that when thepiston 20 operates to bring the bag members 22 together, the clampingprojections 42 will engage first followed by the heating elements 36 andthe spring mounted parts 38 followed by the serrated knife 40 engagingthe bag.

In use then, the motor which drives the advancing rollers advances insteps. Once the rollers 18 have been advanced and stopped the pistons 20are operated and the upright elements 26 are brought together at theopen side of the material 14. Current is applied to the heating element28 to heat seal the edges of the material which is urged against theheating element 28 by the spring mounted part 30. At the same time, themembers 22 are brought together. As the members 22 are brought together,the clamping projections engage the bag material to close it off and thespring mounted parts 38 then urge the material against the heatingelements 36 to heat seal the material in two vertically spacedpositions. The serrated knife 40 then engages the bag to perforatebetween the two seals. The pistons 20 are then operated to retract themembers 22 and arms 24 and the advancing rollers 18 are advanced againwhile compressed air is supplied through the pipe 32. When the cycle hasbeen repeated, the first bag has been created. The bags are created in astrip and can be torn off at the perforated line created by the knife40.

It is seen that the clamping projections act to close off the area beingsealed by the heating element 36 from back pressure from the bag whichhas just been formed so that the seals which are created are notsubjected to that pressure until the seals have been formed and cooledto some degree. In this way a seal is reliably formed.

The supply pipe 32 and the recesses 34 in the rollers 18 are sized andspaced in relation to the thickness of the bag material 14 such thatlittle or no air can escape backwards between the supply pipe 32 and therollers 18 and thus the amount of air supplied to each bag can becontrolled precisely and a uniform series of bags produced.

The supply pipe may supply compressed air at 3 psi. The bag material maybe any suitable heat sealable material which provides an air barrier andmay be low density polyethylene (LDPE), for example. The sealing contacttime may be 1.5 seconds.

The second embodiment is shown in FIG. 3 and is similar to theembodiment of FIGS. 1 and 2. Only the differences from the firstembodiment will be described and the same reference numerals will beused for equivalent features.

The only difference in the second embodiment is that the projections 42are not provided on the bag members 22 but instead are provided onseparately operated rams (not shown). This enables greater andindependent control over the delay between bag clamping and bag sealingand cutting. It also makes the heating elements 36 easier to change.

We claim:
 1. Bag sealing apparatus for producing bags of gas forprotective packing, the apparatus comprising a gas source to pump gastowards an opening in a bag, means for sealing the opening in the bagand means for clamping the bag in an airtight manner downstream of thesealing means to reduce gas back pressure, the clamping means comprisingat least one elongate clamping member having a length greater than thewidth of the bag thereby clamping the bag across substantially itsentire width.
 2. Apparatus as claimed in claim 1, wherein the gas sourceis a source of compressed air.
 3. Apparatus as claimed in claim 1,wherein the sealing means comprises heat sealing means.
 4. Apparatus asclaimed in claim 1, wherein the clamping means comprises a resilientmember which is urged against the bag.
 5. Apparatus as claimed in claim1, wherein the clamping means comprises two resilient clamping membersarranged on opposite sides to clamp a bag between them.
 6. Apparatus asclaimed in claim 1, wherein the clamping means is arranged to clamp thebag before the sealing means starts to seal the bag.
 7. Apparatus asclaimed in claim 1, wherein a clamping member of the clamping means anda sealing member of the sealing means are mounted together on a mountingmember.
 8. Apparatus as claimed in claim 7, wherein on the mountingmember, the clamping member is resiliently mounted ahead of the sealingmember so as to engage the bag before the sealing member.
 9. Apparatusas claimed in claim 7, wherein a second mounting member is providedwhich mounts one of a second clamping member and a second sealingmember.
 10. Apparatus as claimed in claim 9, wherein only one of thefirst and second mounting members is movable.
 11. Apparatus as claimedin claim 9, wherein both of the first and second mounting members aremovable towards and away from each other.
 12. Apparatus as claimed inclaim 7, wherein the or each mounting member is moved pneumatically. 13.Apparatus as claimed in claim 1, wherein the apparatus is arranged tooperate in a cycle.